Rotary disk platen



Feb. 26, 1952 J MlLLER 2,586,848

ROTARY DISK PLATEN Filed July 19, 1945 2 SHEETSSFEET l AZ Zorn/e 5 Feb.26, 1952 2,586,848

ROTARY DISK PLATEN Filed July 19, 1945 2 SX-IEETSSHEET 2 fvveniorPatented Feb. 26, 1952 ROTARY DISK PLATEN Theodore J. Miller, St. Paul,Minn., assignor to Minnesota Mining & Manufacturing Company, St. Paul,Minn., a corporation of Delaware Application July 19, 1945, Serial No.605,962

12 Claims.

This invention relates to supports or anvil members or platens for usein backing up or supporting sheet abrasives at the point where theworkpiece being abraded contacts the abrasive coated side of theabrasive sheet during an abrading operation. V

It is particularly applicable to belt sanding or belt grinding, i. e.,to abrading operations in which an abrasive belt or strip is employed,and the invention is accordingly illustrated in the present disclosurein connection with belt sanding apparatus.

A belt sanding apparatus usually comprises an endless abrasive beltmounted on two or more pulleys, and means for continuously driving thebelt. Abrading operations with such apparatus may be divided roughlyinto two classifications, namely, unsupported operations and supportedoperations. An unsupported operation is where there is no support backof the belt at the point of contact with the work other than the tensionof the belt that is applied between the adjacent pulleys or guides,whereas a supported operation is where there is.

The present invention relates to the latter type of operation, 1. e., tosupported operations.

In the said supported type of operations there are at least twoprincipal types or classes of supports. One is a wheel or pulley,usually one of the driving or idling pulleys aroundwhich the endlessbelt is mounted, the peripheral surface of the pulley being employed tobear against the work. This is sometimes referred to as a roll or linecontact support, and is particularly suited for spot grinding and otherprecision work such as surfacegrinding. The second type of support is ananvil member or platen, usually substantially fiat, which is applied toa span of the belt between two of the pulleys, and it is to this secondor platen type of support that the present invention relates.

' Heretofore the flat platen method of support has caused a decided dropin the efiiciency of the belt long before the mineral on the belt is.worn down or abraded off. This was due largely to a filling and glazingof the belt which developed rapidly early in the life of the belt sothat only the tops of the highest particles'ever came into full use.Some attempts were made to improve thi situation, including the use ofirregular surfaced platens but whatever improvement these may haveproduced in the way of lengthened belt life, was offset by an increasedwearing or hollowing of the platen face.

Neverthelessgbecaus'eof its peculiar adaptability to certain types ofgrinding operations, fiat platen belt grinding must of necessity be usedand it is therefore an objective of this invention to provide a platenor suitable supporting element for flat belt grinding which will provideinter alia (1) longer belt life, (2.) faster cutting and (3) retentionby the platen of its fiat surface.

The present invention does indeed meet these and other objectives andsolves these and other problems successfully, and, in its illustratedaspect comprises a belt-supporting platen having a generally planarworking surface or face mounted adjacent the back of a span of the beltwith the platen face substantially parallel thereto and means for movingthe platen face during an abrading operation in a path substantiallyparallel to the belt span.

The motion of the platen may be effected in various ways, e. g., byoscillation, by providing a platen in the form of a disc and thenrotating it; or by providing a platen in the form of an endless beltpositioned to run in contact with the abrasive belt.

The platen face is discontinuous or broken. It may be broken in avariety of patterns, it being preferable to shape the irregularities orbreaks so as to provide alternate areas of support and non-support forthe belt and so as to produce what may be termed a line contact betweenthe belt and the work.

The invention is exemplified by devices described hereinafter andillustrated in the accompanying drawings in which:

Figure 1 is a schematic view (front) of a belt sanding apparatusemploying a rotary platen;

Figure 2 is a side view of the apparatus of Figure 1, showing aworkpiece being abraded;

Figure 3 is a vertical fragmentary section (enlarged) on the line 3-3 inFigure 1 looking in the direction of the arrows, and showing a workpiecebeing abraded;

Figures 4, 5 and 6 are fragmentary front elevations of rotary platens.

Figure '7 is a side elevation of the platen fragment of Figure 6;

Figure 8 is a schematic view (front) of a belt sanding apparatusemploying an oscillating platen;

Figure 9 is a side view of the apparatus of Figure 8; and

Figure 10 is a schematic view (side) of a belt sanding apparatusemploying an endless belt platen.

Figures 1 and 2 show a belt sanding apparatus comprising an endlessabrasive belt 3-! mounted on rotatable pulleys 2| and 22, means, such asan electric motor (not shown), for rotating the pulleys so as to drivethe belt, and an anvil or supporting member or platen in the form of adisc P-l rotatably mounted, by means of a shaft 23 and bearings 24,adjacent the back of a span of the belt with the face 25 of the disc P-lsubstantially parallel to the span. The face 25 is substantially fiat orplanar with its continuity broken at intervals by a plurality ofdepressions in the form of radially extending elongate aperportion ofthe belt that is opposite a slot2$ (and is thus unsupported) is-.therebyforced to yield slightly in a direction. inwardly: into the slot;whereas the portion of. the. belt thatcontacts the platen face (and isthus. supported). does not so yield, so that the belt isbent slightly.and. there is formed, in effect, a. temporary ridge or bumpru.

in. the. belt in conformity to. the contour of. the edges: (Figure *3).This causes what. may, for convenience, be termed a line contact betweenthe belt and the workpiece, as contrasted with the-fiat 01' surfacecontact that results from continuous or. smooth. surfaced platens, theline being the impact ridge or bumpy whichcorn forms in length,direction, curvature, etc., ape proximately to the edge at. There isconsequently produced an impact together with an increase in pressureper unit area between the belt and the work, which causes thebelt tocut:at each impactmuch more than when there-is simply a sliding frictionalcontact over-a broad area between the surface of the belt-and thesurface of the work. The line contact-thus produces faster cut. It alsoproduces longer belt life-because the bending of the belt at yopensitup, breaks up anyglaze that i has formed, exposes fresh unusedportionof the mineral particles and results in keeping the belt atfullcutting efficiency until its entire coating of abrasive particles issubstantially completely used up. There is'substantially no wastemineral.

The movement of the belt B4 in contact with the platen P-l causes thelatter'to rotate; or, rotation may be effected by suitable driving meanssuch as the electric motorM-l.

One very advantageous result of such movement or rotation of the platenis to distributethe pressure and the consequent-wear of the platen facethroughout its workingarea, thereby preserving the desired overallplanar profile of the Iorking portion of the platen face for a verysubstantial period of time, as contrasted with the rapid localizedhollowing of the ordinary stationary platens. The latter commonly needreplacement in a few hours, whereas rotary platens made in accordancewith my invention have been known to run for several months withoutvariation in the flatness of the working surface.

The depressions or slots 26 need not necessarily pierce the disc as longas the depression is of sufficient depth and with a wall 26a ofsuflicient steepness to form an effective impact edge :12. Also thedepressions may take a wide variety of shapes, sizes, angles, frequencyof occurrence, etc., as shown in Figures 4, 5, 6 and 7, it beingunderstood that the designs as wellas the dimensions and angles thereshown are illustrative and not limiting.

Figure 4 illustrates a preferred embodiment. To compensate for thedifference in linear speed between portions of the disc face that arenear to and far from its center, respectively, the depressions or slots26' are here placed at an angle of 15- to the radial linewhich increasesthe space differential between their outer and inner ends; and each slotis narrowed toward its outer end, thereby decreasing the effectiveimpact of the edge :2 against the work in proportion to the narrowing.The disc of Figure 4 thus provides evencutting acrossthe entire width ofthe workpiece. Also the angular position of the edges 3: in this discprovides something in the nature of a shearingeffect, a point by pointcontact between the belts impact ridge and the leading or upper'edge ofthe workpiece.

Figure 5 shows a still further variation, the depressions, here ,beingcircular apertures or-holes bored, through the disc, such a patternbeing particularly suitable for fine precision grinding.

Figures 6 and 7 show what may. be termed a ridged type disc, carrying onits. surface a plurality of outwardly extending ridgesin spaced relationto.each other, theouter portions of the ridges together forming acomposite surface of substantially planar contouruwhich constitutes theouter orworkingsurface 25" or. theplaten. It comprisesa disc base; 30overlaid with ridges 3| which may be of any shape.in,cross-section. Herethey are. circular,.being; rodsqthat are cut andwelded to. the base 30to. form square depressions or spaces 26 between them, the .rodsthemselves forming atonce the impact edges :c and the platen face 25]..Such a disc isparticularly suitable for-very. fast .andvery, roughabrading or cutting. This. is due. partly to them.- creasein the size of.thebump or impact ridgeyf causedby the. relatively; wider, spacesordepresesions. 26 and partly to the. increasedpressure per square inchbetween. thebelt and the .workpiece caused by the smallertotaLcontactarea.

, Within certain'limits there; is adirect; inverse relationship between.contact. area and cutting.

speed.

From these-few illustrativeexamples it will.

Although movementpf-the platen, preferably in .a plane parallelwiththebelt, is. anessential element of. my invention, such; movement is notconfined; to that. produced/by the :rotation. illus-v tratedandcontemplated. in Figures 1 to.7, but may, for example; .be 'by;oscillation of the platen as shown in Figures ,8 and. 9, orbythemovement of an. endlessbelt: platenras-shown in Figure. 10.

In Figures 8 and 9 the platen P-Z; (in' a belt sanding apparatus 1which. is otherwise. the same asrthatuof Figures '1 and.-2), is,slidably held bya suitable support, I35 andoscillated-or reciprocatedup.and .downby a suitable: driving means,

such asanainengine reciprocator. (not shown) or. thecrank wheel [36andpitmanlfl driven by=the; electric motor M-.-2. The face l25.-of theplaten P-Z, like. that of P-|-, ,ispreferably substantially fiat orplanar, with its-v continuitybroken at intervals by; a plurality; ofdepressions.

I2B.to form impact edges As. in, the; rotary platens of Figures 1 to '7,the -;depressionsof the oscillating platen P-Lof'Figuresj 8-,ands 9. may

have a. wide variety of depths,,sizes, shapea-angularity, frequency ofoccurrence, etc. as. lon as they provide impact edges suitable foroperation on the. principles described above in connection with theimpact edges :1: of Figures 1 and 3.

In Figure the endless belt or saddle belt platen P-3 (in a belt sandingapparatus which is otherwise the same as that of Figures 1, 2,8 and 9)is positioned so that one of its spans serves as the support back of aspan of the abrasive belt B-3 opposite the point where the workpiece W-3is pressed during an abrading operation. It is driven in the samedirection as the abrasive belt 3-3 by reason of its frictional contacttherewith, or itmay be driven by suitable power means, such as theelectric motor M-3, through its supporting pulleys.

The face 225 of the belt platen P-3, like those of the platens P-l andP-2, 'is preferably generally planar with its continuity broken atintervals by a plurality of depressions 226 which may, for example, besuch as to provide a plan and profile like that of the platen face inFigures 8 and 9. The said platen surface may be formed or constructed bymolding; or by cutting the depressions in a smooth surfaced belt, inwhich case the original surface of the belt would become the platen face225; or by fastening strips or patches of suitable material onto a belt,in which case the-original surface of the belt would become the bottomof the depressions and the tops of the ridges or patches would becomethe platen face 225. The belt may be of ordinary power belting material,such as rubberized fabric, leather rubber, etc., or itmay be syntheticrubber or resin, or any hard tough material of sufficient flexibility toserve as an endless belt. As in the rotary platens of Figures 1 to 7 andthe oscillating platen of Figures 8 and 9, the depressions of the saddlebelt platen P-3 of Figure 10 may have a wide variety of depths, sizes,shapes, angularity, frequency of occurrence, etc. as long as theyprovide impact edges suitable for operation on the principles describedabove in comiection with the impact edges :1: of Figures 1 and 3.

When a saddle belt platen is used, the opera: tion is not then, strictlyspeaking, a supported operation. In a sense it is supported, but thesupport is, in turn, simply the unsupported span of a second belt, sothat the effect is to preserve the aspects of unsupported grinding inthe way of yieldability and flexibility while adding the benefit ofadded support over and above that provided by the ordinary tension ofthe abrasive belt.

The cutting efficiency of the various types of broken-surfaced movingplatens of my invention, increases as their linear speed approaches thatof the belt, and substantially beyond that. Their movement may be in thesame direction as that of the belt or it may be in the reversedirection.

It will be seen that sanding platens made in accordance with myinvention possess numerous important and valuable advantages over thoseheretofore known, including (1) longer life of the platen and retentionby the working portion of its exterior surface of the desired overallplanar contour or flatness, due to the movement of the platen; (2) loweror cooler abrading temperatures due to numerous factors, includingreduced friction, the faster cut and the movement of the platen; (3)longer life of the abrasive sheet due to numerous factors including thecooler abrading temperature and the fact that substantially all of theabrasive coating is rendered usable by the opening up effect of theplatens impact edges; and (4) faster out, due to numerous factorsincluding the broken-surface feature and the unique effect of a rotatingdisc platen.

The principle of a broken, irregular or variate surfaced moving platen,as taught by my invention, may be employed in ways other than thosedescribed herein and in connection with abrasive materials andstructures other than belts. For example the invention may be adaptedfor use with abrasive discs by using a broken surfaced back-up padadapted to move or to rotate in relation to the disc.

The invention is not to be understood as restricted to the details setforth since these may be modified within the scope of the appendedclaims without departing from the spirit and scope of the invention.

The construction of platen disclosed in Figures 6 and 7 is claimed in mydivisional application, Ser. No. 212,223, filed Feb. 23, 1951. Theconstruction of platen disclosed in Figures 8 and 9 is claimed in mydivisional application, Ser. No. 225,397, filed May 9, 1951.

I claim:

1. In a belt sanding apparatus which comprises an endless abrasive beltand means for continuous propulsion thereof, a belt-supporting platencomprising a rotatably mounted disc positioned with a portion of asurface thereof adjacent the back of a span of the belt andsubstantially parallel thereto, the said portion of the surface beingsubstantially planar with its continuity interrupted by a plurality ofdepressions, a wall of a depression and a planar surface of the discmeeting to form an edge.

2. In a belt sanding apparatus which comprises an endless abrasive beltand means for continuous propulsion thereof, a belt-supporting platencomprising a rotatably mounted disc positioned with a portion of asurface thereof adjacent the back of a span of the belt andsubstantially parallel thereto, the said portion of the surface beingsubstantially planar with its continuity interrupted by a plurality ofdepressions, a Wall of a depression and the planar surface of the discmeeting at an approximate right angle to form an edge.

3. In a belt sanding apparatus which comprises an endless abrasive beltand means for continuous propulsion thereof, a belt-supporting platencomprising a rotatably mounted disc positioned with a portion of asurface thereof adjacent the back of a span'of the belt andsubstantially parallel thereto, the said portion of the surface beingsubstantially planar with its continuity interrupted by a plurality ofelongate depressions extending outwardly from the central portion of thedisc towards its periphery.

4. In a belt sanding apparatus which comprises an endless abrasive beltand means for continuous propulsion thereof, a belt-supporting platencomprising a rotatably mounted disc positioned with a portion of asurface thereof adjacent the back of a span of the belt andsubstantially parallel thereto, the said portion of the surface beingsubstantially planar with its continuity interrupted by a plurality ofelongate approximately radially disposed depressions.

5. In a belt sanding apparatus which com prises an endless abrasive beltand means for continuous propulsion thereof, a belt-supporting platencomprising a rotatably mounted disc posi- 7 tioned with a portion of asurface-thereof adj acent the-back of a span of the. belt and. substantially parallel thereto, the said portion of the-surface beingsubstantially planar with its continuity broken by a plurality ofapproximately radially disposed depressions, a wall of a depression andthe planar surfacecof the. disc meeting to form an edge.

6. The device-of c1aim5 in whichthedepressio'ns are at an acute; angleto the radii; that intersect, them".

'7. The device; of claim 5. in which the-depressions are narrowedtowardtheir'outer ends and are at an acute: angle; to theradii that.intersect them.

8. In a belt sanding apparatus which comprises an endless, abrasivebeltand means/for continuous propulsion. thereof, a. belt-supporting platencomprising a rotatably mounteddisczpositioned with a portion of asurface? thereof adjacent the back of a span of thebelt andsubstantially parallel thereto, the said portion of the surface beingsubstantially planar with' its continuity interrupted-by a plurality of,circular depressions.

9. In a belt sanding apparatus which comprises an endless abrasive beltand means for continuous propulsion thereof, a belt-supporting platencomprising a rotatably mounted disc positioned with a portion of asurface thereof adjacent the back of a span of the belt andsubstantially parallel thereto, the said portion of the surface beingsubstantially planar with its continuity interrupted by a plurality ofapertures that pierce the disc.

8 10;"The deviceof claim 9 in which the aper tures are elongate;

11'. The device of claimv 9 inwhich the apertures aretcircular."

12. In an abrading operation which comprises propelling.- arr. endlessabrasive belt with a span of: the belt in contact with the workpiece,the stepstcomprising pressing the span against the workpiece with aninterrupted surface. disc platen: and causing the platen face to rotatein relation. to. the, span in a. plane. substantially parallel to: themovement of the span and ate different linear speed.

THEODORE J. MILLER.

REFERENCES CITED The following references are of record in the file-ofthis patent:

v UNITED STATES PATENTS Number Name Date 685,328 Gale Oct. 29, 1901891,251 Harbers June 23, 1908 910,634 Allen Jan. 26, 1909 1,036,783 BeinAug. 2'7, 1912 1,043,194" Blevney Nov. 5, 1912 1,064,572 Trogdon June10, 1913 2,195,340 Potash Mar. 26, 1940 2,232,149 Tautz Feb. 18, 19 41FOREIGN PATENTS Number Country Date 29,731 Sweden June 18, 1909 32,310Sweden Nov. 8, 1910 695,453 Germany Aug. 26, 1940

